Apparatus for forming metal oxide film, method for forming metal oxide film, and metal oxide film

ABSTRACT

A method for forming a metal oxide film, the method including: forming a source solution containing metal into a mist, heating a substrate, supplying the source solution formed into a mist onto a first main surface of the substrate through a first supply path, and supplying hydrogen peroxide through a second path different from the first supply path onto the first main surface of the substrate, where the method further includes, in the following order, preliminarily preparing data showing a relationship among a molar ratio of an amount of the hydrogen peroxide to an amount of the zinc in the source solution, a carrier concentration of the metal oxide film, and a mobility of the metal oxide film, determining an amount of the hydrogen peroxide supplied with the data, and supplying the determined amount of the hydrogen peroxide through the second path onto the first main surface of the substrate.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.13/643,380, filed on Oct. 25, 2012, which is a 35 U.S.C. 371 nationalstage patent application of international patent applicationPCT/JP10/059243, filed on Jun. 1, 2010, the entire content of which isincorporated by reference.

TECHNICAL FIELD

The present invention relates to an apparatus for forming a metal oxidefilm that forms a metal oxide film on a substrate, and a method forforming a metal oxide film. Further, the present invention relates to ametal oxide film formed by the method for forming a metal oxide film.

BACKGROUND ART

In the fields of solar cells, light emitting devices, touch panels,sensors, and the like, metal oxide films are formed on substrates.Conventionally, Patent Documents 1, 2, and 3 disclose the technique offorming a metal oxide film on a substrate.

In the technique of Patent Document 1, a metal oxide film is formed on asubstrate by bringing a solution in which a metal salt or a metalcomplex is dissolved into contact with a heated substrate. In thistechnique, the solution contains at least one of an oxidizing agent anda reducing agent.

In the technique of Patent Document 2, a tetrabutyltin solution or a tintetrachloride solution, in which hydrogen peroxide is added as anoxidizing agent, is sprayed onto a preheated substrate and thermallydecomposed. Then, after the substrate temperature lowered by spraying ofthe solution returns, the solution is sprayed repeatedly. Accordingly, athin film of tin oxide is grown on the surface of the substrate.

In the technique of Patent Document 3, a solution in which a thin filmmaterial is dissolved in a volatile solvent is intermittently sprayedtoward a substrate kept hot from above to form a transparent conductivefilm on the surface of the substrate. In this technique, intermittentspraying is high-speed pulsed intermittent spraying in which onespraying duration is 100 milliseconds or less.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Laid-Open No. 2007-109406

Patent Document 2: Japanese Patent Application Laid-Open No. 2002-146536

Patent Document 3: Japanese Patent Application Laid-Open No. 2007-144297

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

If a material having high reactivity is selected in forming a meal oxidefilm on a substrate, the material reacts with oxygen and moisture in theatmosphere and is decomposed. Meanwhile, if a material stable in theatmosphere is selected, as to the temperature for forming a metal oxidefilm, a substrate needs to be heated at high temperature. Under presentcircumstances, there is desired a technique of heating a temperature atlower temperature, to thereby form a metal oxide film having lowresistance on a substrate.

Therefore, an object of the present invention is to provide an apparatusfor forming a metal oxide film that forms a metal oxide film having lowresistance through a low temperature treatment, and a method for forminga metal oxide film. Further, the present invention provides a metaloxide film formed by the method for forming a metal oxide film.

MEANS TO SOLVE THE PROBLEM

In order to solve the above-mentioned problem, an apparatus for forminga metal oxide film according to the present invention includes: a firstcontainer storing a source solution containing metal; a second containerstoring hydrogen peroxide; a reaction chamber in which a substrate isdisposed, including a heating unit heating the substrate; a first pathconnecting the first container and the reaction chamber, for supplyingthe source solution from the first container to the reaction chamber;and a second path connecting the second container and the reactionchamber, for supplying the hydrogen peroxide from the second containerto the reaction chamber.

Further, a method for forming a metal oxide film according to thepresent invention includes the steps of: (A) forming a source solutioncontaining metal into a mist; (B) heating a substrate; (C) supplying thesource solution formed into a mist in the step (A) onto a first mainsurface of the substrate in the step (B); and (D) supplying hydrogenperoxide through another path different from a supply path for thesource solution onto the first main surface of the substrate in the step(B).

EFFECTS OF THE INVENTION

In the present invention, a heated substrate is supplied with a sourcesolution containing metal and is also supplied with hydrogen peroxidethrough a channel different from that for the source solution. Thisenables to form a metal oxide film having low resistance on a first mainsurface of a substrate even if the substrate is heated at lowtemperature.

The object, features, aspects, and advantages of the present inventionwill be more apparent from the following detailed description inconjunction with the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a schematic configuration of an apparatus 100for forming a metal oxide film according to a first embodiment.

FIG. 2 is a view for describing a method of producing a solution 11 inwhich an amount of hydrogen peroxide is adjusted.

FIG. 3 is a figure showing the relationships among the carrierconcentration of a metal oxide film, mobility of the metal oxide film,and molar ratio of H₂O₂/Zn.

FIG. 4 is a view showing a schematic configuration of an apparatus 150for forming a metal oxide film according to a third embodiment.

FIG. 5 is a view showing a schematic configuration of an apparatus 200for forming a metal oxide film according to a fourth embodiment.

FIG. 6 is a view showing a schematic configuration of an apparatus 250for forming a metal oxide film according to the fourth embodiment.

FIG. 7 is a view showing a schematic configuration of an apparatus 500for forming a metal oxide film, which causes a source solution tocontain hydrogen peroxide and a metal source and supplies the sourcesolution to a substrate.

FIG. 8 is a figure showing experimental results (sheet resistance—molarratio) in which the apparatus 500 for forming a metal oxide film wasused.

FIG. 9 is a figure showing experimental results (film thickness—molarratio) in which the apparatus 500 for forming a metal oxide film wasused.

FIG. 10 is a figure showing experimental results (sheetresistance—heating temperature) in which the apparatus 150 for forming ametal oxide film was used.

FIG. 11 is a figure showing experimental results (sheet resistance—molarratio) in which the apparatus 150 for forming a metal oxide film wasused.

FIG. 12 is another figure showing experimental results (sheetresistance—molar ratio) in which the apparatus 150 for forming a metaloxide film was used.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention is specifically described withreference to the drawings showing embodiments thereof.

First Embodiment

FIG. 1 is a view showing a schematic configuration of an apparatus 100for forming a metal oxide film according to a first embodiment.

As shown in FIG. 1, the apparatus 100 for forming a metal oxide filmaccording to the first embodiment is configured of a reaction chamber 1,a heating unit 3, a first solution container 5A, a second solutioncontainer 5B, a first mist forming unit 6A, a second mist forming unit6B, a first path L1, and a second path L2.

In the film forming apparatus 100, a spray pyrolysis method, a pyrosolmethod, a mist deposition method, or the like is performed. That is, inthe film forming apparatus 100, a predetermined solution formed into amist is sprayed onto a first main surface of a substrate 2, so that apredetermined metal oxide film can be formed on the first main surfaceof the substrate 2.

The substrate 2 being a film-formed body, on which a metal oxide film isformed, is provided in the reaction chamber 1. The heating unit 3 isdisposed in the reaction chamber 1, and the substrate 2 is placed on theheating unit 3 (alternatively, the substrate 2 is provided apart fromthe heating unit 3 in the reaction chamber 1 so as to face the heatingunit 3). A metal oxide film is formed on the first main surface of thesubstrate 2 being heated by the heating unit 3.

As is apparent from this description, the first main surface of thesubstrate 2 which is referred to in the present specification is themain surface of the substrate 2 on a side on which the metal oxide filmis formed. On the other hand, a second main surface of the substrate 2which is referred to in the present specification is the main surface ofthe substrate 2 on a side being in contact with the heating unit 3.

During the film forming treatment for a metal oxide film, the reactionchamber 1 is in a non-vacuum (that is, at atmospheric pressure).

A glass substrate, a resin substrate, a film, and the like used in thefields of solar cells, light-emitting devices, touch panels, and flatpanel displays such as liquid crystal panels can be employed for thesubstrate 2.

A heater or the like can be employed for the heating unit 3, which canheat the substrate 2 placed on the heating unit 3 (or facing the heatingunit 3). The heating temperature of the heating unit 3 is adjusted by anexternal controller (not shown) included in the film forming apparatus100, so that the heating unit 3 is heated to a metal oxide film formingtemperature during the film forming treatment.

Stored in the first solution container 5A is a source solution 10containing metal. The first mist forming unit 6A is provided onto thebottom of the first solution container 5A. For example, an ultrasonicatomizer can be employed for the first mist forming unit 6A. The firstmist forming unit 6A can form the source solution 10 in the firstsolution container 5A into a mist.

While the configuration in which each mist forming unit is disposed onthe bottom of each solution container is described herein, the place inwhich each mist forming unit is provided is not necessarily limited tothe bottom of each solution container.

The source solution 10 contains an alkoxide compound, a β-diketonecompound, an organic salt compound, an inorganic salt compound, or thelike as a metallic element containing compound.

The metal source contained in the source solution 10 may beappropriately selected in accordance with the use of a metal oxide filmformed. For example, titanium (Ti), zinc (Zn), indium (In), tin (Sn), orthe like can be employed as the metal source.

The source solution 10 is not necessarily required to contain a dopantsource. However, it is preferable that the source solution 10 contain atleast any one of boron (B), nitrogen (N), fluorine (F), aluminum (Al),phosphorus (P), gallium (Ga), arsenic (As), niobium (Nb), indium (In),antimony (Sb), bismuth (Bi), vanadium (V), and tantalum (Ta) as thedopant source.

Water, alcohols such as ethanol and methanol, and mixed solutionsthereof can be employed for the solvent of the source solution 10.

As shown in FIG. 1, the first solution container 5A and the reactionchamber 1 are connected to each other via the first path L1. The sourcesolution 10 formed into a mist by the first mist forming unit 6A issupplied from the first solution container 5A to the reaction chamber 1through the first path L1. The supplied source solution 10 is splayedonto the first main surface of the substrate 2 disposed being heated inthe reaction chamber 1.

Meanwhile, stored in the second solution container 5B is a solution 11containing hydrogen peroxide. The second mist forming unit 6B isprovided onto the bottom of the second solution container 5B. Forexample, an ultrasonic atomizer can be employed for the second mistforming unit 6B. The second mist forming unit 6B can form the solution11 in the second solution container 5B into a mist.

Water, alcohols such as ethanol and methanol, and mixed solutionsthereof can be employed for the solvent of the solution 11.

The description has been given of the mode in which the source solution10 in the first solution container 5A contains a predetermined dopant.In place of the source solution 10 containing the dopant, the solution11 in the second solution container 5B may contain the dopant.

As shown in FIG. 1, the second solution container 5B and the reactionchamber 1 are connected to each other via the second path L2. As isapparent from FIG. 1, the second path L2 is a path providedindependently of the first path L1. The solution 11 formed into a mistby the second mist forming unit 6B is supplied from the second solutioncontainer 5B to the reaction chamber 1 through the second path L2. Thesupplied solution 11 is splayed onto the first main surface of thesubstrate 2 being heated in the reaction chamber 1.

As described above, the first path L1 and the second path L2 are pathsindependently of each other. Accordingly, the source solution 10containing metal and the solution 11 containing hydrogen peroxide aresupplied to the reaction chamber 1 through different systems. Then, thesource solution 10 and the solution 11 are mixed together in thereaction chamber 1.

The source solution 10 and the solution 11 supplied to the reactionchamber 1 react with each other on the substrate 2 being heated, wherebya predetermined metal oxide film is formed on the first main surface ofthe substrate 2. The metal oxide film formed is a transparent conductivefilm of indium oxide, zinc oxide, tin oxide, or the like, which dependon the type of the metal source contained in the source solution 11.

The source solution 10 and solution 11 unreacted in the reaction chamber1 are always (continuously) discharged out of the reaction chamber 1.

Further, as shown in FIG. 2, the film forming apparatus 100 includes acontainer 51 and a container 52 separately. The container 51 storeshydrogen peroxide 11 a. Meanwhile, the container 52 stores a component11 b other than the hydrogen peroxide 11 a of the solution 11.

The film forming apparatus 100 is externally operated for producing thesolution 11. This operation is aimed for adjusting and determining thecontent of the hydrogen peroxide 11 a in the solution 11. The operationis executed on the film forming apparatus 100, so that a predeterminedamount of the hydrogen peroxide 11 a is delivered from the container 51and another predetermined amount of the component 11 b is delivered fromthe container 52. Accordingly, the hydrogen peroxide 11 a and thecomponent 11 b each output are supplied to the second solution container5B, and the solution 11 containing the hydrogen peroxide 11 a of acontent determined through the above-mentioned operation is produced inthe second solution container 5B.

Next, the method for forming a metal oxide film according to the presentembodiment is described.

First, the hydrogen peroxide 11 a and the component 11 b are mixedtogether, to thereby produce the solution 11. Here, the source solution10 containing a predetermined molar amount of zinc as a metal source isprepared in the first solution container 5A.

The film forming apparatus 100 is provided with an input part (notshown) for inputting/selecting the content of hydrogen peroxide in thesolution 11. A user performs the operation of inputting or selecting adesired value as the content of hydrogen peroxide on the input part.Then, a first amount of the hydrogen peroxide 11 a according to theoperation is delivered from the container 51. Meanwhile, a second amountof the component 11 b according to the operation is delivered from thecontainer 52. Then, the hydrogen peroxide 11 a and the component 11 beach delivered are supplied to the second solution container 5B, wherebythe solution 11 is produced in the second solution container 5B. Here,the content of hydrogen peroxide in the produced solution 11 is adesired value in the operation.

The inventors have found that the relationships shown in FIG. 3 existamong the molar ratio (=H₂O₂/Zn) of the content of hydrogen peroxide inthe solution 11 (amount of hydrogen peroxide supplied to the reactionchamber 1) to the amount of zinc contained in the source solution 10,the carrier concentration of the metal oxide film formed, and themobility of the metal oxide film formed.

The vertical axis on the left side in FIG. 3 represents the carrierconcentration (cm⁻³) of the metal oxide film formed. The vertical axison the right side in FIG. 3 represents the mobility (cm²/V·s) of themetal oxide film formed. The horizontal axis in FIG. 3 represents themolar ratio (=H₂O₂/Zn) of amount of substance of hydrogen peroxide(H₂O₂) to amount of substance of zinc (Zn). “Square marks” in FIG. 3indicate data values showing the relationship between the molar ratioand the carrier concentration. “Triangular marks” in FIG. 3 indicatedata values showing the relationship between the molar ratio and themobility.

FIG. 3 reveals that the carrier concentration of the metal oxide filmformed decreases along with an increase of the content of hydrogenperoxide in the solution 11 to the content of zinc in the sourcesolution 10. Further, FIG. 3 reveals that the mobility of the metaloxide film formed increases along with an increase of the content ofhydrogen peroxide in the solution 11 to the content of zinc in thesource solution 10.

As is well known, the resistivity of a metal oxide film formed isproportional to the inverse of carrier concentration×mobility.

Therefore, data shown in FIG. 3 is prepared in advance prior to theproduction of the solution 11. Then, the user considers that thephysical properties (such as transmittance) of the metal oxide film arechanged by changing the resistivity, mobility and carrier concentrationof a metal oxide film formed. In the case of the operation ofselecting/inputting the content of hydrogen peroxide, the user takes theabove into consideration and then determines the content of hydrogenperoxide in the solution 11 in accordance with the use of the metaloxide film formed, using the data shown in FIG. 3. In other words, theuser determines the amount of hydrogen peroxide supplied to the reactionchamber 1 using the data shown in FIG. 3.

The source solution 10 is prepared in the first container 5A, and thesolution 11 is prepared in the second container 5B, so that the sourcesolution 10 is formed into a mist by the first mist forming unit 6A inthe first solution container 5A, and the solution 11 is formed into amist by the second mist forming unit 6B in the second solution container5B.

The source solution 10 formed into a mist is supplied to the reactionchamber 1 through the first path L1. Meanwhile, the solution 11 formedinto a mist is supplied to the reaction chamber 1 through the secondpath L2 that is a path different from the first path L1.

Meanwhile, the substrate 2 being in contact with the heating unit 3 isheated to a metal oxide film forming temperature by the heating unit 3,and the temperature of the substrate 2 is maintained at the metal oxidefilm forming temperature. For example, the temperature of the substrate2 is maintained at 300° C. or lower.

The source solution 10 formed into a mist and the solution 11 formedinto a mist are supplied to the first main surface of the substrate 2being heated as descried above. Accordingly, a predetermined metal oxidefilm is formed on the first main surface of the substrate 2 located inthe reaction chamber 1.

As described above, in the present embodiment, the source solution 10containing metal and the solution 11 containing hydrogen peroxide aresupplied to the reaction chamber 1 through different paths. Then, thesource solution 10 and the hydrogen peroxide (solution 11) are broughtinto contact with the substrate 2 being heated in the reaction chamber1.

Therefore, a metal oxide film having low resistivity can be formed onthe first main surface of the substrate 2 even if the heatingtemperature of the substrate 2 is low. This effect is described in afifth embodiment below with reference to experimental data.

In the present embodiment, the data shown in FIG. 3 is prepared inadvance, and the amount of hydrogen peroxide to the amount of zinccontained in the source solution 10, which is supplied to the reactionchamber 1, is determined by using the data.

Therefore, the carrier concentration and mobility of a metal oxide filmformed can be adjusted, whereby it is possible to provide a metal oxidefilm having physical property values according to the use.

As described above, the source solution 10 or the solution 11 maycontain a dopant. Depending on the conductivity type of a dopant, ametal oxide film (transparent conductive film) being an n-typesemiconductor can enter an electron-richer state. In this case, theelectric resistance of a metal oxide film (transparent conductive film)formed can be lowered more. Further, it is conceivable that a metaloxide film may be a p-type semiconductor depending on the conductivitytype of the dopant. In the metal oxide film being a p-typesemiconductor, a hole serves as a carrier to become conductive, whichincreases the usefulness thereof as a light-emitting device rather thanas a transparent conductive film.

Second Embodiment

In a second embodiment, the source solution 10 described in the firstembodiment further contains ammonia or ethylenediamine.

That is, in the film forming apparatus 100 shown in FIG. 1, the firstsolution container 5A stores the source solution 10 further containing apredetermined amount of ammonia or a predetermined amount ofethylenediamine.

Then, the first mist forming unit 6A forms the source solution 10further containing ammonia or ethylenediamine into a mist. Then, thesource solution 10 formed into a mist is supplied to the reactionchamber 1 through the first path L1. As described also in the firstembodiment, in this case, the substrate 2 is heated to a metal oxidefilm forming temperature in the reaction chamber 1.

The configuration of the film forming apparatus 100 and the operation inthe film forming method other than the above are similar to thosedescribed in the first embodiment.

As described above, in the present embodiment, the source solution 10containing ammonia (or ethylenediamine) in addition to metal is formedinto a mist. Then, in the reaction chamber 1, the source solution 10formed into a mist is brought into contact with the heated substrate 2.

Accordingly, it is possible to further improve the production efficiencyof the metal oxide while maintaining low resistance of a metal oxidefilm formed. That is, the source solution 10 further contains ammonia(or ethylenediamine), leading to improvement of the film forming rate ofa metal oxide film. Through the improvement of the film forming rate, itis possible to form a metal oxide film having a predetermined filmthickness in a short time.

Third Embodiment

FIG. 4 is a view showing a schematic configuration of an apparatus 150for forming a metal oxide film according to a third embodiment.

As is apparent from the comparison between FIGS. 1 and 4, the apparatus150 for forming a metal oxide film according to the present embodimenthas a configuration in which an ozone generator 7 is added to theconfiguration of the apparatus 100 for forming a metal oxide filmaccording to the first embodiment. In addition, a third path L3 isdisposed in a film forming apparatus 200 for supplying ozone from theozone generator 7 to the second solution container 5B.

The other configuration is similar to the descriptions above in thefirst and second embodiments except that the ozone generator 7 and thethird path L3 are additionally provided.

The ozone generator 7 can generate ozone. The ozone generated in theozone generator 7 is supplied to the second solution container 5Bthrough the third path L3. Then, the supplied ozone is supplied towardthe first main surface of the substrate 2 in the reaction chamber 1through the second path L2, together with the solution 11 containinghydrogen peroxide.

In the ozone generator 7, for example, an oxygen molecule is decomposedby applying high voltage between parallel electrodes disposed inparallel and passing oxygen between the electrodes, and the oxygenmolecule couples with another oxygen molecule, so that ozone isgenerated.

When ozone, the misty solution 11, and the misty source solution 10 aresupplied to the reaction chamber 1, the ozone, the solution 11, and thesource solution 10 react with each other on the substrate 2 beingheated, whereby a predetermined metal oxide film is formed on the firstmain surface of the substrate 2. The ozone, solution 11, and sourcesolution 10 unreacted in the reaction chamber 1 are always(continuously) discharged out of the reaction chamber 1.

Next, a method for forming a metal oxide film according to the presentembodiment is described.

First, as described in the first embodiment (see FIGS. 2 and 3), theamount of hydrogen to the content of a metal source contained in thesource solution 10, which is supplied to the reaction chamber 1, isdetermined. Then, the solution 11 containing hydrogen peroxide isproduced in the second solution container 5B based on the determinedamount.

The source solution 10 and the solution 11 are prepared in the firstsolution container 5A and the second solution container 5B,respectively, and then, ozone is generated in the ozone generator 7. Inthe first solution container 5A, the first mist forming unit 6A formsthe source solution 10 into a mist. In the second solution container 5B,the second mist forming unit 6B forms the solution 11 into a mist.

The generated ozone is supplied to the second solution container 5Bthrough the third path L3. Then, the ozone and the misty solution 11 aresupplied to the reaction chamber 1 through the second path L2. The mistysource solution 10 is supplied to the reaction chamber 1 through thefirst path L1. As described in the first embodiment, the second path L2through which hydrogen peroxide passes is different from the first pathL1 through which the source solution 10 containing metal passes.

Meanwhile, the substrate 2 being in contact with the heating unit 3 isheated to a metal oxide film forming temperature by the heating unit 3,and the temperature of the substrate 2 is maintained at the metal oxidefilm forming temperature. For example, the temperature of the substrate2 is maintained at approximately 200° C.

The ozone, the source solution 10 containing metal, and the solution 11containing hydrogen peroxide are supplied to the first main surface ofthe substrate 2 being heated. The contact of the ozone and the solutions10 and 11 with the substrate 2 being heated causes thermal decompositionof the ozone, which produces an oxygen radical. The oxygen radicalaccelerates the decomposition of the source solution 10, so that apredetermined metal oxide film is formed on the first main surface ofthe substrate 2.

As described above, the ozone generator 7 that generates ozone to besupplied to the reaction chamber 1 is also provided in the presentembodiment.

Therefore, ozone and active oxygen produced as a result of thedecomposition of ozone due to heat or the like are highly reactive, andaccordingly, the decomposition and oxidation of material compound in thesource solution 10 are accelerated. This enables to form a metal oxidefilm having low resistance on the substrate 2 even in a state in which aheating temperature is lower compared with the first embodiment.

Also in the present embodiment, the source solution 10 may containammonia or ethylenediamine as described in the second embodiment.Alternatively, the source solution 10 or the solution 11 may contain adopant as described in the first embodiment. The metal contained in thesource solution 10 is appropriately selected depending on the type of ametal oxide film to be formed. Still alternatively, the amount ofhydrogen peroxide to the amount of zinc contained in the solution 10,which is supplied to the reaction chamber 1, may be determined inaccordance with the use of a metal oxide film (zinc oxide film) to beformed, as described with reference to FIGS. 2 and 3.

Fourth Embodiment

The present embodiment describes modifications of the third embodiment.FIGS. 5 and 6 show the modifications of the film forming apparatusincluding the ozone generator 7 described in the third embodiment.

In the apparatus 200 for forming a metal oxide film shown in FIG. 5, theozone generator 7 is connected to the reaction chamber 1 by means of thethird path L3. The ozone generated in the ozone generator 7 is suppliedto the reaction chamber 1 through the third path L3. As is apparent fromthe comparison between FIGS. 4 and 5, in the film forming apparatus 200,the ozone passes through the third path L3 provided independently of thefirst and second paths L1 and L2.

Therefore, the source solution 10 containing metal, the solution 11containing hydrogen peroxide, and the ozone are supplied to the reactionchamber 1 in which the substrate 2 being heated is disposed through thefirst path L1, the second path L2, and the third path L3, respectively.

The other configuration and operation of the film forming apparatus 200are similar to the description in the third embodiment.

In an apparatus 250 for forming a metal oxide film shown in FIG. 6, theozone generator 7 is connected to the reaction chamber 1 by means of thethird path L3. The ozone generated in the ozone generator 7 is suppliedto the reaction chamber 1 through the third path L3. Further, acontainer 21 is provided. The container 21 stores a gas 18 containinghydrogen peroxide of a predetermined concentration. The second path L2connecting the container 21 to the reaction chamber 1 is provided. Thegas 18 in the container 21 is supplied to the reaction chamber 1 throughthe second path L2. The film forming apparatus 250 is further providedwith another solution container 5D that stores a solution 19 containinga dopant. The another solution container 5D is connected to the reactionchamber 1 by means of another path L4. The solution 19 in the anothersolution container 5D that is formed into a mist by another mist formingunit 6D is supplied to the reaction chamber 1 through the another pathL4.

That is, as is apparent from the comparison between FIGS. 4 and 6, thefilm forming apparatus 250 is different from the film forming apparatus150 in the following points.

In the film forming apparatus 250, ozone passes through the third pathL3 provided independently of the paths L1, L2, and L4. In place ofpreparing liquid hydrogen peroxide (see container 21 and gas 18) andsupplying the misty hydrogen peroxide to the reaction chamber 1, in thefilm forming apparatus 250, gaseous hydrogen peroxide is prepared, andthe hydrogen peroxide is supplied to the reaction chamber 1 as the gas.The film forming apparatus 250 is also provided with the second path L2for supplying gaseous hydrogen peroxide independently of the first pathL1 through which the source solution 10 is supplied.

The film forming apparatus 250 is provided with the another solutioncontainer 5D that stores the solution 19 containing a dopant and theanother path L4 for transferring the solution 19. That is, the anothersolution container 5D and the another path L4 are elements dedicated toa dopant.

Therefore, in a case where the supply of a dopant to the reactionchamber 1 is omitted, the film forming apparatus 250 may not be providedwith the elements including the another solution container 5D and theanother path L4. Also in a case where the supply of a dopant to thereaction chamber 1 is not omitted, if the source solution 10 contains adopant as well, the film forming apparatus 250 may not be provided withthe elements including the another solution container 5D and the anotherpath L4.

In the film forming apparatus 250, the source container 10 containingmetal, the gas 18 containing hydrogen peroxide, and the ozone aresupplied to the reaction chamber 1 in which the substrate 2 being heatedis disposed through the first path L1, the second path L2, and the thirdpath L3, respectively, and the solution 19 containing a dopant issupplied thereto through the another path L4.

The other configuration and operation of the film forming apparatus 250are similar to the description in the third embodiment.

Fifth Embodiment

The present embodiment describes the experimental data showing theeffects of the present invention.

Comparative Example

First, the experimental results in a case of using a film formingapparatus 500 shown in FIG. 7 are described before describing theeffects of the present invention.

In the film forming apparatus 500 shown in FIG. 7, a solution container5 stores a source solution 31. The source solution 31 contains not onlymetal but also hydrogen peroxide. The source solution 31 formed into amist by a mist forming unit 6 is supplied to the reaction chamber 1through one path L. That is, in the film forming apparatus 500, hydrogenperoxide and a metal source of a film to be formed are supplied to thereaction chamber 1 through the same system.

The experiment of forming a zinc oxide film on the first main surface ofthe substrate 2 was conducted using the film forming apparatus 500.FIGS. 8 and 9 show the experimental results.

In the experiment, the source solution 31 in which ZnAcac₂ (zincacetylacetonate)=0.02 mol/L and MeOH (methanol)/H₂O (water)=9 was used,and the heating temperature of the substrate 2 was set to approximately300° C. Further, the source solution 31 contained hydrogen peroxide, andthe content of the hydrogen peroxide was varied in the range where H₂O₂(hydrogen peroxide)/Zn (zinc)=0 to 10 (specifically, the content of zincwas constant, where H₂O₂/Zn=0, 0.1, 0.5, 1, 2, 5, 10).

FIG. 8 shows the results of the measurement of the sheet resistance ofeach zinc oxide film formed on the substrate 2 by varying the content ofhydrogen peroxide in the source solution 31. In FIG. 8, the verticalaxis represents a sheet resistance (Ω/sq.) and the horizontal axisrepresents H₂O₂/Zn (molar ratio).

As shown in FIG. 8, in the case of using the film forming apparatus 500,the sheet resistance of a zinc oxide film formed sharply increases alongwith an increase of the content of hydrogen peroxide in the sourcesolution 31. In the measurement where H₂O₂/Zn=2, the sheet resistance ofa zinc oxide film formed exceeded the range of the vertical axis in FIG.8 (as described below, a zinc oxide film is not formed if H₂O₂/Zn=5 orlarger.

That is, as is apparent from the results of FIG. 8, in a case of usingthe film forming apparatus 500 supplying hydrogen peroxide and metalthrough the same system, a zinc oxide film having low resistance couldnot be formed, but a zinc oxide film having considerably high resistancewas formed.

FIG. 9 shows the results of the measurement of the film thickness ofeach zinc oxide film formed on the substrate 2 by varying the content ofhydrogen peroxide in the source solution 31. In FIG. 9, the verticalaxis represents a film thickness (nm) and the horizontal axis representsH₂O₂/Zn (molar ratio). Also in FIG. 9, the content of zinc was constant,whereas the content of hydrogen peroxide was varied.

As shown in FIG. 9, in the case of using the film forming apparatus 500,the film thickness of a zinc oxide film formed decreases along with anincrease of the content of hydrogen peroxide in the source solution 31.In the measurements where H₂O₂/Zn=5 or larger, a zinc oxide film was notformed on the substrate 2.

Experimental Result 1

FIG. 10 is a figure showing the experimental results using the filmforming apparatus 150 described in the third embodiment (see FIG. 4).

In “Experimental result 1”, the source solution 10 contains not only ametal source but also ammonia, a dopant, and the like. Specific filmforming conditions in “Experimental result 1” are as follows.

That is, the source solution 10 in which ZnAcac2=0.02 mol/L,GaAcac3=0.03 mol/L, NH₃ (ammonia solution) 28%=3 mL (in 100 mL ofsolution), and MeOH/H₂O=9 was used. Further, the solution 11 containinghydrogen peroxide of an amount that satisfies H₂O₂/Zn (content of zincin the source solution 11)=25 in which MeOH/H₂O=9 was used. The flowrate of ozone supplied to the reaction chamber 1 was 10 mg/min.Moreover, the heating temperature of the substrate 2 was varied from145° C. to 287° C.

FIG. 10 shows the results of the measurement of the sheet resistance ofeach zinc oxide film formed on the substrate 2 by varying the filmforming temperature for the substrate 2. In FIG. 10, the vertical axisrepresents a sheet resistance (Ω/sq.) and the horizontal axis representsthe temperature (° C.).

FIG. 10 also shows the results obtained by employing the film formingconditions described above except that hydrogen peroxide was notsupplied (omitting the container 5B in FIG. 4). Specifically, in FIG.10, white triangular marks indicate the experimental result data in thecase where the hydrogen peroxide was supplied, whereas black diamondmarks indicate the experimental result data in the case where thehydrogen peroxide was not supplied.

As shown in FIG. 10, at the film forming temperatures except for 287° C.at which the substrate 2 was heated, the sheet resistance of a metaloxide film formed reduced more in the case where hydrogen peroxide wassupplied. Further, in the case where hydrogen peroxide was supplied, ametal oxide film having sufficiently low resistance could be producedeven at a low film forming temperature (approximately 200° C.).

Experimental Result 2

FIG. 11 is a figure showing the experimental results using the filmforming apparatus 150 described in the third embodiment (see FIG. 4).

In “Experimental result 2”, the source solution 10 contains not only ametal source but also ammonia, a dopant, and the like. Specific filmforming conditions in “Experimental result 2” are as follows.

That is, the source solution 10 in which ZnAcac2=0.04 mol/L,GaAcac3=0.06 mol/L, NH₃ (ammonia solution) 28%=3 mL (in 100 mL ofsolution), and MeOH/H₂O=9 was used. Further, the solution 11 containinghydrogen peroxide of an amount that satisfies H₂O₂/Zn (the content ofzinc in the source solution 11)=0 to 49 where MeOH/H₂O=9 was used.Specifically, the content of hydrogen peroxide in the solution 11 wasvaried so as to satisfy H₂O₂/Zn=0, 5, 12, 15, 20, 24, 37 and 49 (contentof zinc was constant). The flow rate of ozone supplied to the reactionchamber 1 was 10 mg/min. Moreover, the heating temperature of thesubstrate 2 was approximately 200° C.

FIG. 11 shows the results of the measurement of the sheet resistance ofeach zinc oxide film formed on the substrate 2 by varying the content ofhydrogen peroxide in the solution 11. In FIG. 11, the vertical axisrepresents a sheet resistance (Ω/sq.) and the horizontal axis representsH₂O₂/Zn (molar ratio).

FIG. 11 shows the measurement results in both cases where ozone wassupplied to the reaction chamber 1 and where ozone was not supplied tothe reaction chamber 1 (the film forming conditions were the same inboth cases except for the presence/absence of the ozone supply). In FIG.11, white triangular marks indicate the experimental result data in thecase where ozone was supplied, whereas black diamond marks indicate theexperimental result data in the case where ozone was not supplied.

As shown in FIG. 11, in the case where ozone was supplied, a metal oxidefilm having sufficiently low resistance could be formed at the low filmforming temperature (approximately 200° C.). In the case where ozone wassupplied, the resistance of a metal oxide film formed tends to decreasealong with an increase of the amount of hydrogen peroxide in the areawhere H₂O₂/Zn does not exceed 12. Meanwhile, in the area where H₂O₂/Znis 12 or larger, the resistance of a metal oxide film formed isapproximately constant even if the amount of hydrogen peroxide isincreased.

As shown in FIG. 11, even in a case where ozone was not supplied, as isapparent from the comparison with FIG. 8, the sheet resistance of ametal oxide film formed maintains a sufficiently low resistance evenwhen the amount of hydrogen peroxide was increased.

As shown in FIG. 11, in a case where ozone was not supplied, a zincoxide film having a sheet resistance equal to or smaller than the sheetresistance of a zinc oxide film formed in the case where hydrogenperoxide was not contained (case where the vertical axis in FIG. 11 iszero) could be formed in the area in which H₂O₂/Zn is 20 or smaller.

Experimental Result 3

FIG. 12 is a figure showing the experimental results using the filmforming apparatus 150 described in the third embodiment (see FIG. 4).

In “Experimental result 1” and “Experimental results 2”, a dopant of apredetermined conductivity type was contained in the source solution 10.On the other hand, in “Experimental result 3”, the solution 11containing hydrogen peroxide contains a dopant of a predeterminedconductivity type. Specific film forming conditions in “Experimentalresult 3” are as follows.

That is, the source solution 10 in which ZnAcac2=0.04 mol/L, NH₃(ammonia solution) 28%=3 mL (in 100 mL of solution), and MeOH/H₂O=9 wasused. Further, the solution 11 containing gallium of an amount thatsatisfies GaAcac3=0.0008 mol/L and containing hydrogen peroxide of anamount that satisfies H₂O₂/Zn (the content of zinc in the sourcesolution 11)=0 to 4.9 where MeOH/H₂O=9 was used. Specifically, thecontent of hydrogen peroxide in the solution 11 was varied so as tosatisfy H₂O₂/Zn=0, 0.5, 1, 2.5, and 4.9 (the content of zinc wasconstant). The flow rate of ozone supplied to the reaction chamber 1 was10 mg/min. Moreover, the heating temperature of the substrate 2 wasapproximately 200° C.

FIG. 12 shows the results of the measurement of the sheet resistance ofeach zinc oxide film formed on the substrate 2 by varying the content ofhydrogen peroxide in the solution 11. In FIG. 12, the vertical axisrepresents a sheet resistance (Ω/sq.) and the horizontal axis representsH₂O₂/Zn (molar ratio).

As shown in FIG. 12, a metal oxide film having sufficiently lowresistance could be formed at a low film forming temperature(approximately 200° C.). Further, similarly to the tendency shown inFIG. 11, the resistance of a metal oxide film formed decreases alongwith an increase of the amount of hydrogen peroxide.

In the experimental results shown in FIG. 11, if H₂O₂/Zn=5, the sheetresistance of a metal oxide film formed was 2200 (Ω/sq.) in a case whereozone was supplied. In “Experimental result 2” where the results of FIG.11 were obtained, the source solution 10 contained a dopant of apredetermined conductivity type.

On the other hand, as shown in FIG. 12, the sheet resistance of a metaloxide film formed was 630 (Ω/sq.) or lower in “Experimental Result 3” inwhich the solution 11 contained a dopant of a predetermined conductivitytype. That is, the sheet resistance of a metal oxide film formed becomessmaller in the case where the solution 11 contains a dopant comparedwith the case where the source solution 10 contains a dopant.

On both of the film forming conditions for “Experimental result 2” andthe film forming conditions for “Experimental result 3”, ZnAcac₂=0.04mol/L. On the other hand, Ga/Zn=0.15 on the film forming conditions for“Experimental result 2”, whereas Ga/Zn=0.02 on the film formingconditions for “Experimental result 3”. That is, it is understood thatthe sheet resistance of a metal oxide film formed became smaller in“Experimental result 3” compared with “Experimental result 2” althoughthe amount of a dopant decreased more in “Experimental result 3”compared with “Experimental Result 2”.

While the present invention has been described above in detail, theforegoing description is in all aspects illustrative, and the presentinvention is not limited thereto. That is, numerous modifications andvariations can be devised in the described aspects without departingfrom the scope of the invention.

Description of Reference Symbols  1 reaction chamber  2 substrate  3heating unit  5A first solution container  5B second solution container 5D another solution container  6A first misting unit  6B second mistingunit  6D another misting unit  7 ozone generator 10 source solution 11solution 18 gas (containing hydrogen peroxide) 19 solution (containingdopant) 21 container L1 first path L2 second path L3 third path L4another path 100, 150, 200, 250 apparatus for forming metal oxide film

1. A method for forming a metal oxide film, the method comprising:forming a source solution comprising metal into a mist; heating asubstrate; supplying the source solution formed into a mist onto a firstmain surface of the substrate in the heating, through a first supplypath; and supplying hydrogen peroxide through a second path differentfrom the first supply path onto the first main surface of the substratein the heating, wherein the method further comprises, in the followingorder: preliminarily preparing data showing a relationship among a molarratio of an amount of the hydrogen peroxide to an amount of the zinc inthe source solution, a carrier concentration of the metal oxide film,and a mobility of the metal oxide film; determining an amount of thehydrogen peroxide supplied with the data, and supplying the determinedamount of the hydrogen peroxide through the second path onto the firstmain surface of the substrate, wherein the substrate is arranged underatmospheric pressure, the source solution is converted into a mist by anultrasonic atomizer, and the metal is zinc. 2-3. (canceled)
 4. Themethod according to claim 1, wherein the source solution furthercomprises ammonia.
 5. The method according to claim 1, wherein thesource solution further comprises ethylenediamine.
 6. The methodaccording to claim 1, further comprising supplying ozone onto the firstmain surface of the substrate in the heating.
 7. The method according toclaim 2, wherein the supplying of the source solution and the supplyingof hydrogen peroxide do not comprise supplying ozone onto the first mainsurface of the substrate in the heating, and the molar ratio is 20 orsmaller.
 8. The method according to claim 1, wherein the supplying ofthe hydrogen peroxide further comprises supplying a dopant of apredetermined conductivity type onto the first main surface of thesubstrate with the hydrogen peroxide through the second path.
 9. Themethod of claim 1, wherein the source solution comprises boron,nitrogen, fluorine, aluminum, phosphorus, gallium, arsenic, niobium,indium, antimony, bismuth, vanadium, tantalum, or any combinationthereof.
 10. The method of claim 1, wherein the source solutioncomprises water, an alcohol, or a mixed solution thereof.